A SUCCINCT history was given by M. G. Dary, in a recent number of L'Électricien, of the vain efforts that have been made at different times to steer balloons in the atmosphere. Some of the experiments were, indeed, of real merit; but they did not succeed practically, because the problem they were intended to solve offers insurmountable obstacles. The steering of balloons and the realization of great speed with them are practically impossible, and the results obtained from experiments directed to those objects have not been worth the immense outlays that have been made upon them. Yet balloons styled directable will probably render very appreciable services in military art and under a few other special circumstances. The experiments of M. Gaston Tissandier and Commandant Renard have not been useless, and it will be of some advantage to continue them. But while balloonists are right in seeking to increase the dimensions of their globes in order to increase at once the proportion of ascensional power and of motor and propulsive energy to resistance, we, advocates of machines heavier than the air, looking especially to great speed, would gradually diminish the function of the balloon as a sustainer, reduce it, and bring into greater predominance the propulsory organs, making them at once more powerful and lighter. These are those which, with the motor and the generator, represent the element heavier than the air. When the balloon shall have been eliminated in this way, practical aërial navigation will have been accomplished.

Let us suppose ourselves looking through a glass, eye at the eye-piece, at a balloon. It is large, gigantic, monstrous, the aërostat of to-day. Turn the glass, end for end. The balloon is reduced, and becomes a mere point, imperceptible, lost. Such is, from our point of view, the balloon of the morrow. It is well for the present to use the balloon as a supplementary sustaining instrument; but let us always keep in mind that we shall thank it as soon as possible for its services and show it the door. A hypothesis should be to the physicist simply a provisional artifice for the convenient grouping or explaining of a number of determined phenomena; and, to our view, a balloon is a similar artifice, the present uses of which may be valuable.

We had the honor some years ago of becoming acquainted with MM. de la Landelle and Ponton d'Amécourt, warm partisans and advocates of the doctrine of machines heavier than the air, which originated, according to classical traditions, with Architas. They convinced us, and we have since been their fervent disciple. We are, in fact, a persistent admirer of the simple processes employed in Nature and used in a marvelous way by birds to sustain themselves in the air and guide their flight, and specious calculations have never caused us to doubt the possibility of a solution of the problem of locomotion in the air by wholly mechanical means; and we have long regarded the solution of it as depending solely on the discovery of a powerful and light motor. How many examples does the history of natural philosophy present us of calculations that have deceived—either because their starting-point was false, or because we were mistaken in interpreting the results!

What good does it do to descant on the forms and the details of an air-machine when its most essential part, its soul we might say—its motor—has not been found? Could we give a rational theory of telephony before Bell invented his electric telephone, or of the transmission of force to great distances before the creation of the Gramme machine?

We have received numerous letters during the last twenty years from authors and inventors desiring to submit to us their projects and arrangements of propellers. "It is all very well," we have told them, "but, before sending me anything—have you a motor?" "A motor? No, sir; we have thought about it, indeed, but have depended on you for that," "If I had a motor," I would reply, "I should have no need of your apparatus; I have a thousand of them, and my only trouble is in choosing between them." The motor, in fact, is the essential thing; having that, it is a minor affair whether one prefers the aëroplane, the helicopter, or the aviator; it is a question of return—a question that must be looked into, but which is strictly subordinate to the nature of the motor. It is not till that is got that calculation should come in, when it can find a sure starting-point, based on well-conducted experiments and precise ideas, and its results will be susceptible of an immediate verification. We have constantly employed this prudent, positive method, and it only can give satisfactory results. This motor, which is to fulfill at the same time the two conditions so hard to reconcile, of great power and extreme levity, we shall now try to describe.

Fig. 1.—Bird-like Generator-Motor and Propeller.

The fact indisputably results from observations, from the positive experiments of M. Marey, from the studies of M. Espitalier, and from our personal labors, that birds expend on an average a motor exertion of 75 kilogrammes per unity of weight—a unity comprehended between 3·6 and 12·5 kilogrammes—in rising vertically one metre per second. Observe that we are talking of gross work, not of useful work effected directly upon the air. Thus Goupil, a respected authority, has found that the work of a horsepower in the pigeon is given for a weight of 12·5 kilogrammes. That is the manifest work, but not the work really developed by the animal; the wing, like the screw, in fact, makes only a weak return.

We select, then, the minimum unity of weight 3·5 kilogrammes per horse-power which results from the experiment with our electrical helicopter, because we know in advance that we can not obtain the full return for the expenditure; and in this weight we must include that of the generator of energy, or of the propeller, and all the accessories.

It is impossible, in this necessarily brief study, to give the names of all the known motors, and still less of the apparatuses which might be applied as motors. Inventors reserve many surprises in that matter. But, without letting imagination carry us beyond the domain of experimental science, it is allowable for us to consider what satisfaction steam, electricity, and such accumulators of energy as India rubber, steel, compressed air, gas motors, and explosives may give. We are able now, with special precautions, to construct steam motors of extreme levity, and giving one horse-power for a weight very near that of 3·5 kilogrammes; but if we add to them the indispensable generator and the inevitable propeller, the weight increases in formidable proportions, and the system becomes inapplicable to any mode of support in the air.

Electricity, although it is better in many respects, is likewise liable to criticism. Yet we had the honor of performing some satisfactory experiments with it in 1887 at the Scientific Congress in Toulouse, and in 1888 at the Easter session of the Société de Physique. We had taken all possible care in the construction of a motor; it was all of aluminum, with the exception of the poles, which were of soft iron. Its weight was ninety grammes, and its power, measured with our dynamometer, was maintained at two kilogrammetres, corresponding exactly with one horse-power per 3·375 kilogrammes. This motor, armed with a light and geometrically Fig. 2.—Electric Helicopter and Aëroplane. perfect helix, made according to a new method which we had explained to the Academy of Sciences on the 12th of July, 1886, was placed in one of the plates of a balance, and put in connection, with a constant electrical source of forty watts, when it raised its whole weight. In order to render more visible the extent of the result, and obtain a more exact idea of it, I arranged a light balance with long arms, to one of which I attached the motor experimented on, as in Fig. 2. The electric communications, carried through the foot, knife-edges, and arms of the balance, can not obstruct the freedom of its motion. Being movable in the vertical and horizontal directions, the balance changes immediately from the position A B to that of A' B'. The power developed by the motor is found, by the most careful measurement, equivalent to two kilogrammes—a power so related to the weight of the motor as to be capable of raising it vertically twenty-two metres in a second. The simple theoretical calculation deduced from the experimental fact assigns 3·375 kilogrammes to the motor that will develop seventy-five kilogrammes. But so minute a motor returns only about twenty per cent of the energy which is confided to it, while a motor of from fifty to one hundred horsepower will return eighty, ninety, or one hundred per cent. It is possible, therefore, and seems to be reasonable, that a large electric motor, the power of which increases faster than the weight, would employ the surplus of sixty or seventy per cent in raising the generator, the propeller, and the aëronaut. We do not intend to hypothecate the future and form tables on gratuitous suppositions, probable as they may seem. We therefore, for the moment, lay aside the electric motor, because, with its generator and propeller, it exceeds the weight of 3·5 kilogrammes per horse-power, which we have imposed upon ourselves as the minimum.

We now come to accumulators of energy. India rubber, for example, the elasticity of which is often utilized as a reservoir of power, and has a potential, in this point of view, fifteen times superior to that of steel, furnishes power and motion together. Joining to it an immediate organ of resistance to the air, we have an apparatus heavier than air. Penaud chose admirably; and one of the first helicopters was formed upon this plan. But, while India rubber stores a large sum of energy, it expends it faster than it obtains it, and can not of itself renew the provision. Penaud had only a small success with it, because the thongs he used were placed and displaced too slowly; and if he had found a means of changing them more rapidly, the considerable charge of his provision would have made him lose the primary advantages of his judicious choice.

Compressed air motors and gas motors enjoy a certain repute which is in many respects deserved; but as they are constructed, they require the assistance of lubricating and refrigerating apparatus which have weight, and are thus excluded for the present from the list of applications for aerial locomotion. So there are no steam motors, or electric motors, or accumulators of energy like India rubber, or steel, or compressed air motors or generators, that fully answer the requirements. None of them, as they are, supply such coexisting conditions of power and levity as are strictly imposed by the nature of the problem. Is it, then, true that there is now no motor with its accessories, the generator and propeller, which can be used at once, or at least improved upon, for the purpose we have in view? The comparative experiments which we have reported, and have verified with our new universal direct-reading dynamometer, which we had the honor of presenting to the Academy on the 23d of June, 1891, seem to attest this. Still, if the generator and propeller, mutually necessary. are the organs that embarrass us, can we not find some substitute?

The electrical helicopters, with which we have obtained excellent results, seem to offer a special adaptation of the screw to the motor, which, like all electric motors, turns with an excessive velocity—so that one of the organs seems made for the other. We have often been struck, in our electric boats, with the fact that the wake at the stern is hardly perceptible. This is because the helix of our steering motor-propeller, having the great velocity of twenty-four hundred turns in a minute, enters the water as a screw its tap. In our electric helicopter, likewise, the screw forms, we might say, an integral part of the motor, thus supplying us with a motor-propeller, India rubber offers a still more perfect connection between the accumulator of potential and the motor—the generator or accumulator and the motor being absolutely identical. India rubber is a generator-motor. Hence, since we can not eliminate the generator or the propeller from the apparatus we imagine, we will absorb them and fuse them into the motor. We will create a new organism sufficing for itself, and will call it the generator-motor-propeller. We have ourself devised a propeller of this kind, by the aid of the well-known Bourdon tube, an instrument which is the essential part of the Bourdon manometers. Electricity plays in it a part only secondary, but necessary. This apparatus has so far given us satisfaction, and it may be that it will serve for some time as the essential basis of machines heavier than the air.

If the pressure of the gas contained in the tube increases, the tube changes shape, and its elliptical branches tend to spread apart; while, if the pressure is diminished, inverse action takes place, and the branches approach. If, then, we provoke a series of alternate condensations and expansions, or increasing and diminishing pressures, in the interior of the tube, it will go through a series of oscillations, of strong vibrations, capable of being used as a motor force, chiefly and perhaps only in the conditions under which we have placed ourselves. For the purpose of further increasing the energy of the resistance of the tube, and also of diminishing the volume of the chamber in which the explosions are produced, we have inclosed in the interior a similar second tube—an addition which augments the elastic force of the engendered gases, while diminishing the expenditure of combustibles. The whole of the system is represented by Fig, 1, and was presented by us to the Academy of Sciences in December, 1870,

The wings A and B are fixed directly, but with a rotary motion, at the vibrating ends of the tube, suppressing all intermediary organs of transmission by friction or rotation. Depression of the wings corresponds to condensed pressures, and elevation to dilated pressures. The chemical combination made use of is the oxidation of hydrogen. Hydrogen is easily obtained, rapidly, in great quantities, and pure, and oxygen for burning it is already prepared in the atmosphere. Our bird, like the birds of Nature, therefore draws a considerable part of its food from the atmosphere. The detonating mixture is regulated at will, but it is nearly twenty-five parts of hydrogen to seventy-five parts of atmospheric air, while the inflammation of it is produced by electricity, as in gas machines. In the small model (Fig. 1) the generator of explosions is a revolver barrel (D), armed with twelve cartridges, the charge of which has been carefully determined; to make the catches perform and the barrel turn, the bird must be left to itself, while the cock is kept raised simply by the weight of the apparatus. To start the machine, it is suspended by a cord fixed at the end of a crane (Fig. 3), while the pendulum thus composed

Fig. 3.—Arrangements for starting the Bird.

is withdrawn from the vertical and held by a second cord against the foot of the crane. Two candles, one movable (A) and the other fixed (B), placed in the verticals of the points of attachment, are intended to burn the two cords.

When we burn the first cord with the candle A, the bird, like Foucault's pendulum, begins an oscillation. It goes, describing the arc of a circle, from the position 1 to the position 2, reaching there with a horizontal velocity, when the candle B is applied and burns the suspending cord. The hammer is released and falls, the cartridge explodes, the tube vibrates strongly, and the wings falling sweep the air vigorously; at the same time the bird abandons its first horizontal position, and with its inclined tail takes on a slight movement of ascension (position 3). Thus the disengaged gases escape into the atmosphere, in the inverse direction of the movement, so as to utilize their reaction. The vibrating tube resumes its original shape, and the wings rise. Promptly, the barrel, carried on by its cog-work, brings a cartridge under the hammer, which falls; a second explosion is produced, and the phenomena already described are repeated in their order. During the third, fourth, and so on to the twelfth explosion, the bird flies over a horizontal distance of seventy-five or eighty metres, sustaining itself against gravity and steadily rising. Instead of the bird falling straight down at the end of its course, the wings, kept up by the drawing together of the branches of the tube and the silken aëroplane (C, Fig. 1), the surface of which is proportioned to the weight of the imitation animal, act as a parachute, and the apparatus descends obliquely and slowly. The aëroplane, which is represented by dotted lines, connects the head of the bird with the helm, and with the wings and the tail. The use of the aëroplane will always be of advantage, whatever the power of the motor; for its surface, constantly proportionate to the total weight, will serve to prevent any accident in case of the sudden arrest of the motor machine. We repeat that, in the apparatus of large dimensions, a reservoir of compressed hydrogen is substituted for the cartridges of the small model; while the use of aluminum is suggested by its lightness and the probability of its being obtainable at a reasonable price. We also remark that the extensive cooling surface of the vibrating tube and its direct contact with the air, which will be closer as the velocity is greater, will keep it at a moderate temperature; yet there will be little danger of its getting heated, for the simplicity of the mechanism, and the removal of all transmission by rotation or sliding, will prevent the necessity of using lubricants or refrigerants. In short, the combined advantages of the generator-motor-propeller constitute it the lightest aviator that it is possible to construct. It possesses, we dare say, all the warrantees of ascensional power and return.

We shall be glad if we have succeeded in this summary in conveying to our readers the faith we have in the possibility and the near realization of practical navigation of the air; if the subject has any further interest for them, they will find a general serious and profound discussion of it in a book by M, Barral, and also full descriptions of a number of sustaining machines which we have devised, including the one we have just presented to them. Constructed during the siege of 1870, it is the first machine heavier than the air susceptible of construction on a large scale and capable of traveling by its own force. The crowning experiment in the navigation of the air now depends only on capital and secondary studies; and, again, in centering our efforts on the discovery of a strong and light motor, we believe we were the first (in 1870) to set forth the problem correctly. We close by saying, with Victor Hugo, "The future is with navigation of the air."—Translated for The Popular Science Monthly from Le Monde de la Science et de l'Industrie.